An experimental study of drying behaviour in ice patterns formed during spin freezing and its influence on the freeze-drying process

An experimental study on formation of ice patterns during spin freezing of liquid in vials and the effect of such ice patterns in the freeze-drying process is investigated. The process is carried out in vials for liquids such as distilled water and skimmed milk which are immersed and spun in a temperature control bath maintained at -25 °C. The occurrence of different ice patterns are demonstrated using two vials with l/d ratio of 2.4 (V₁) and 3.9 (V₂) with the liquid fill volume varied between 20% and 85%. It is observed that depending on the l/d ratio, speed of rotation and fill volume, different ice patterns such as spiral, cone shape and uniform annular patterns occur. Also, the subsequent drying process effectively depends on the type of ice pattern that resulted in the freezing process. Among the different ice patterns, the uniform annular pattern exhibited a better drying rate.